Unfortunately I have tried looking for a good solution to this myself, and have come up empty handed. Most of the software that I have found requires you to purchase it othewise the trials will place watermarks all over it that can't be removed, or they won't process the entire document.
As Nogg3r5 said, PDF's aren't really designed to be edited but it is possible if you have the right software, unfortunately you would have to purchase the software in order to get it done right.